It is a common demultiplexing problem in optical systems to have an optical signal containing multiple wavelengths each at a different wavelength from which one or more individual channels must be extracted. The traditional solution to this problem has been to employ a wavelength specific demultiplexing device to extract the required wavelengths. Referring to FIG. 1, shown is an example of such a wavelength specific demultiplexer, generally indicated by 11. The input to the demultiplexer is a group of wavelengths having wavelength λ1, . . . , λ64. In order to extract four particular wavelengths, λA,λB,λC,λD, the demultiplexer 11 is provided which extracts those specific wavelengths and passes them to respective receivers 12,14,16 and 18. The demultiplexer 11 is specifically designed for the particular wavelengths λA,λB,λC,λD which are being extracted. Typically the demultiplexer 11 and four receivers 12,14,16 and 18 might be delivered on a card 10. In order to allow the demultiplexing of any arbitrary four wavelengths from a set of a possible 64, it would be necessary to inventory 635,376 different such cards. More realistically perhaps, given the recent propensity towards grouping wavelengths into bands of consecutive wavelengths, in order to allow the demultiplexing of any consecutive group of four wavelengths in a 64 wavelength system, for example {λ1, . . . , λ4}, {λ5, . . . , λ8}, {λ61, . . . , λ64} there would be a requirement to inventory 16 different demultiplexer cards.
This same problem exists on the multiplexing side, namely that a large number of wavelength specific devices must be manufactured and inventoried in order to provide multiplexing flexibility.
Optical networks are commonly deployed as inter-connected optical rings carrying dense wavelength division multiplexed (DWDM) optical signals. As these rings become larger and carry more traffic, interconnection issues increase. The lowest cost method of interconnecting two optical rings is to optically couple them using optical-to-optical (OOO) coupling. Such direct coupling (OOO) of optical rings leads to systems with enormous complexity. The optical wavelength (“color”) assignment is common for both rings. To overcome color blocking, wavelengths cannot be reused locally within each ring therefore link engineering becomes very complex.
Wavelength conversion is necessary to effectively deal with color blocking issues. Recently, all-optical (OOO) wavelength conversion technology has been developed but such technology is not yet cost-effective. The alternative is optical-to-electrical-to-optical (OEO) wavelength conversion. Conventional OEO wavelength converters require filtering to get wavelength-specific. To control costs, such wavelength converters often use fixed filters, with the attendant disadvantage of the many indirect costs associated with network planning, down time due to reconfigurations, inventory along the value chain and sparing. Fixed filters also have the disadvantage of increasing the variants of components in a network and this drives up inventory levels because each variant needs to be stocked individually.